It's unclear when -- if ever -- automakers will equip cars with vehicle-to-vehicle communication systems that would prevent fender benders at intersections.

But one supplier, Qualcomm Technologies Inc., is developing such a system to help motorists avoid pedestrians and cyclists.

Chris Borroni-Bird, Qualcomm's vice president of strategic development, says the company is developing a portable device that would broadcast the position of a pedestrian or cyclist. A properly equipped vehicle would receive the signal and warn the driver if a pedestrian or cyclist is in the vehicle's path.

Qualcomm and other companies are examining such systems at a time when the National Highway Traffic Safety Administration is conducting a major test of vehicle-to-vehicle accident avoidance systems in Ann Arbor, Mich.

The test is going well, researchers say. But it's too early to tell whether such systems will prove practical. And it's unclear whether an aftermarket device such as Qualcomm's is ready for prime time.

As Borroni-Bird notes, Qualcomm's device has a couple of catches. First, it will require a GPS system that can more precisely determine the pedestrian's or cyclist's location. Second, Qualcomm's engineers have to minimize the occurrence of false alerts.

If motorists are falsely warned about impending accidents, they will soon turn off the device, Borroni-Bird says.

The bottom line: The industry has been tantalized by the prospect of communications devices that would prevent collisions. But it could be a while before this technology is road-worthy.